Limit transition handling to displays with desktop mode support

Also simplify the code by checking early if there is a trigger task we
can rely on to determine what needs to happen.

Fix: 405412244
Test: atest ActivityLifecycleTopResumedStateTests
Test: atest DesktopTasksControllerTest
Flag: EXEMPT (bug fix)
Change-Id: I235277d701e385d3969ce33cf52a52d5edaf90d7